Scheduling method and apparatus

ABSTRACT

Disclosed herein are a scheduling apparatus and method. The scheduling apparatus includes a network topology configuration unit and a scheduling unit. The network topology configuration unit configures a network topology that connects nodes to which rank values have been allocated based on a sink node. The scheduling unit schedules data transmission over an uplink and a downlink in a first region and a second region defined in each slot frame based on the rank values obtained based on the sink node. The first region and the second region have different time offsets within the slot frame.

BACKGROUND 1. Technical Field

The present invention relates generally to a scheduling apparatus andmethod, and more particularly to a scheduling apparatus and method thatcan minimize negotiations between nodes within a network.

The present invention has been derived from research conducted forProject for Research into Resilient/Fault-Tolerant Autonomous NetworkingTechnology based on the Physical Attributes, Relationships and Roles ofIoT Devices sponsored by the Korean Ministry of Science, ITC and FuturePlanning and the Institute for Information & Communications TechnologyPromotion [Project Management Number: No. B0190-16-2017] and Project forthe Promotion of University ICT Research Centers sponsored by the KoreanMinistry of Science, ITC and Future Planning and the Institute forInformation & Communications Technology Promotion [Project ManagementNumber: IITP-2017-R0992-17-1023] in 2016.

2. Description of the Related Art

Recently, interest in a ubiquitous computing environment in which allthings are equipped with computing, sensing, and communication functionshas increased. A ubiquitous computing environment has attractedattention as the core technology of sensor network technology thatperforms the functions of detecting and controlling environments outsidehumans.

A wireless sensor network based on such a ubiquitous computingenvironment, e.g., ZigBee, is wireless communication technologydeveloped for wireless application services for civil and industrialfields requiring low power, low cost and small amounts of data. ZigBeedefines network, security and application layers, i.e., higher-levellayers, based on the IEEE 802.15.4 standard that defines a physicallayer and a medium access control (MAC) layer, i.e., layers lower thanthe network layer.

Recently, such a wireless sensor network has been applied to Internet ofThings (IoT) communication, and has been used for communication betweena plurality of nodes. Nodes for the construction of a wireless sensornetwork may implement a network by using a centralized method or adistributed method.

For example, when a network is implemented using the centralized method,a single representative node controls the scheduling operations of allnodes present in the same network. When a single node controls overallcommunication within a network as described above, the correspondingnode requires large amounts of information. Accordingly, in the networkconstructed using the centralized method, when there is a rapid changein a network topology, the transfer of large amounts of data from allnodes to a representative node is required for scheduling, and thus itis impossible to deal with this situation. Furthermore, disadvantagesalso arise in that all the nodes require additional energy and bandwidthresources attributable to the transfer of the data to the representativenode and a long period of time is required for the initialization of thenetwork.

Furthermore, when a network is implemented using the distributed method,all nodes themselves perform scheduling operations. In this case, eachof the nodes must communicate with adjacent nodes in order to avoid acollision that occurs when interfering nodes use the same channel at thesame time. This network requires a specific negotiation protocol. In thecase where a network is constructed using the centralized method, allinformation is collected at a central node and scheduling is determined,whereas in the case where a network is constructed using the distributedmethod, all the nodes within the network collect small amounts ofinformation from adjacent nodes and perform scheduling via a separatenegotiation protocol. As a result, the network implemented using thedistributed method is more robust to a rapid change in a networktopology than the network implemented using the centralized method.However, each of the nodes must submit to additional traffic during theprocess of negotiation with adjacent nodes, and thus consumes additionalenergy and network resources. Furthermore, from the point of view of theoverall network, the network implemented using the distributed methodhas the disadvantage of lacking visibility because scheduling cannot beperformed based on the overall network.

In order to overcome these disadvantages, there has been a need for anetwork which can minimize negotiations between nodes on a wirelesssensor network and which can also minimize collisions attributable todata transmission between nodes.

Accordingly, there is a need for a technology for overcoming theabove-described problems.

Meanwhile, the above-described background technology corresponds totechnical information that has been possessed by the present inventor inorder to contrive the present invention or that has been acquired in theprocess of contriving the present invention, and cannot be necessarilyviewed as a well-known technology that had been known to the publicbefore the filing of the present invention.

SUMMARY

An object of embodiments disclosed herein is to propose a schedulingapparatus and method that can minimize negotiations between nodes withina network.

An object of embodiments disclosed herein is to propose a schedulingapparatus and method that can minimize collisions attributable to datatransmission between nodes within a network.

According to an aspect of the present invention, there is provided ascheduling apparatus, including: a network topology configuration unitconfigured to configure a network topology that connects nodes to whichrank values have been allocated based on a sink node; and a schedulingunit configured to schedule data transmission over an uplink and adownlink in a first region and a second region defined in each slotframe based on the rank values obtained based on the sink node; whereinthe first region and the second region have different time offsetswithin the slot frame.

According to another aspect of the present invention, there is provideda scheduling method for a scheduling apparatus, the scheduling methodincluding: configuring a network topology that connects nodes to whichrank values have been allocated based on a sink node; and schedulingdata transmission over an uplink and a downlink in a first region and asecond region defined in each slot frame based on the rank valuesobtained based on the sink node; wherein the first region and the secondregion have different time offsets within the slot frame.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a block diagram showing a scheduling apparatus according to anembodiment of the present invention;

FIG. 2 is a diagram showing a network topology according to anembodiment of the present invention;

FIG. 3 is a diagram showing a slot frame according to an embodiment ofthe present invention;

FIG. 4 is a flowchart showing a scheduling method according to anembodiment of the present invention;

FIG. 5 is a diagram showing the allocation of slot frames based onuplink and downlink scheduling according to an embodiment of the presentinvention;

FIG. 6 is a diagram showing cells allocated to nodes through schedulingin a network topology according to an embodiment of the presentinvention;

FIG. 7 is a diagram showing data flows based on uplink and downlinkscheduling at the second node shown in FIG. 6; and

FIG. 8 is a diagram showing the allocation of cells within a slot framebased on uplink and downlink scheduling at a node according to anembodiment of the present invention.

DETAILED DESCRIPTION

Various embodiments of the present invention will be described in detailbelow with reference to the accompanying drawings. The embodiments thatwill be described below may be practiced in various different modifiedforms. In order to more clearly describe the features of theembodiments, detailed descriptions of components and functions that arewell known to those having ordinary knowledge in the art to which thefollowing embodiments pertain will be omitted. Furthermore, in thedrawings, the illustration of portions unrelated to the embodiments willbe omitted. Throughout the specification, similar reference symbols willbe assigned to similar components.

Throughout the specification and the claims, when one component isdescribed as being “connected” or “coupled” to another component, theone component may be “directly connected” or “directly coupled” to theother component, or may be “connected” or “coupled” to the othercomponent via a third component. Furthermore, when one component isdescribed as “comprising” or “including” another component, the onecomponent may not exclude a third component but may include a thirdcomponent unless otherwise described.

Embodiments of the present invention will be described in detail belowwith reference to the accompanying drawings.

Prior to the following description, terms that will be used below aredefined first.

In the following description, the term “node” refers to an object whichhas a communication function on a network and which may be connected toother nodes and communicate data. For example, in a sensor network, anode may be each sensor. Furthermore, one of all nodes on a network,which is a node based on which a network topology is configured, isreferred to as a sink node. The sink node may be a reference node thatis placed at the highest location of the network topology.

Terms requiring descriptions, other than the terms defined above, willbe described separately in the following description.

FIG. 1 is a block diagram showing a scheduling apparatus 100 accordingto an embodiment of the present invention.

As shown in FIG. 1, the scheduling apparatus 100 may include a networktopology configuration unit 110, a scheduling unit 120, and a dataprocessing unit 130. For example, the scheduling apparatus 100 may beimplemented in each of all nodes included in a network, or may beimplemented via a plurality of nodes included in a network.

The network topology configuration unit 110 may configure a networktopology by connecting all the nodes within the network based on a sinknode.

For example, the network topology configuration unit 110 may use theIPv6 routing protocol for low-power lossy networks (hereinafter referredto as “RPL”) in a network layer in order to configure network topology.As described above, when the network topology configuration unit 110uses the RPL protocol, data transmission for separate negotiationsbetween all the nodes within the network is not required. In this case,the network topology configuration unit 110 may transmit and receive aDestination Oriented Directed Acyclic Graph (DODAG) Information Object(hereafter referred to as the “DIO”), a DODAG Information Solicitation(hereafter referred to as the “DIS”), and a DODAG Advertisement Object(hereafter referred to as the “DAO”) between the nodes. In this case,the DIO is a message that is adapted to generate and maintain an upwardroute. The DIS is a message that is transmitted to receive DestinationOriented Directed Acyclic Graph (DODAG) Information Objects (hereafterreferred to as the “DIOs”) from adjacent nodes. The DAO is a messagethat is adapted to maintain a downward route.

This enables the network topology configuration unit 110 to be allocateda hop count-based rank by a sink node. In this case, the rank is linkquality between nodes, and refers to a hop count from the sink node oran expected transmission count. When the network topology configurationunit 110 connects to an RPL tree network, it can find the media accesscontrol (MAC) addresses of its own parent node and child nodes.

Therefore, the network topology configuration unit 110 can find the rankvalue of a corresponding node. Assuming that the rank is a hop count, areference node implemented by the network topology configuration unit110 may identify a node, having a rank value smaller than that of thereference node by 1, as a parent node, and may identify a node, having arank value larger than that of the reference node by 1, as a child node.

Furthermore, the network topology configuration unit 110 may use RPL(routing protocol for low-power lossy networks) as a network layerprotocol, and may use time slotted cell scheduling (hereinafter referredto as “TSCH”)-based 802.15.4e as a link layer protocol.

The sink node periodically transmits a beacon signal (for example, aTSCH enhanced beacon). When each of the nodes, other than the sink node,receives a beacon signal, the node may be connected to a TSCH networkformed by the sink node.

Meanwhile, in TSCH, an absolute slot number (hereinafter referred to asthe “ASN”) is used. The ASN refers to a value which is set to 0 when thesink node forms its own network and which is increased by 1 for eachtime slot. Accordingly, the scheduling unit 120 may find the sequentialposition of a period corresponding to a current slot frame by using theASN and the length of the slot frame.

The scheduling unit 120 schedules data transmission and reception overan uplink and a downlink in the tree topology that connects nodes towhich rank values have been allocated based on the sink node. In thiscase, the scheduling unit 120 may classify nodes as a node having an oddrank value or a node having an even rank value. Through this, thescheduling unit 120 may perform scheduling so that data may betransmitted and received over the links of nodes having odd and evenrank values in each of regions having different time intervals in theslot frame.

In this case, the scheduling unit 120 may include an uplink scheduler121 configured to schedule an uplink data and a downlink scheduler 122configured to schedule downlink data.

The uplink scheduler 121 performs uplink scheduling adapted to transmitdata in the direction of the sink node (for example, to transmit data tothe parent node). For example, in a sensor network, a general nodegenerates data including sensing information at intervals of apredetermined period, and transmits the data to a sink node.Accordingly, the uplink scheduler 121 may transmit data, includingsensing information generated at a current node and sensing informationreceived via a child node, to the parent node or sink node with the sinknode set as a final destination.

The downlink scheduler 122 performs downlink scheduling adapted totransmit data in the direction opposite to the sink node (for example,to transmit data to a child node). Accordingly, the downlink scheduler122 may receive a data packet received from the parent node, and mayreceive the packet itself when the destination of the packet is its ownnode and transmit the data in the direction of a child node when thedestination of the packet is the child node.

Meanwhile, when the scheduling unit 120 is implemented in the sink node,the uplink scheduler 121 may transmit received data to a related serveror the like in the network topology implemented in a tree form based onthe sink node, and the downlink scheduler 122 may transmit data,received from the server or the like, to a corresponding node that isconnected to the network topology implemented in a tree form.

The data processing unit 130 may provide data generated at the currentnode or data received from another node to the scheduling unit 120 sothat the scheduling unit 120 can schedule the data. The data processingunit 130 may identify the destination node of the received data, and mayprovide information for data transmission to the scheduling unit 120 sothat the data can be transmitted to the destination node. Furthermore,when the processing of data is required, the data processing unit 130may process the corresponding data, and may store data generated duringthe data processing, data waiting for transmission, or the like. Forthis purpose, the data processing unit 130 may contain memory, or mayuse memory present outside the data processing unit 130.

The data processing unit 130 may transmit or receive data or may reduceenergy in a sleep mode, according to a schedule made by the schedulingunit 120. For example, when the corresponding node is scheduled toperform message transmission and reception in a specific time slot, thedata processing unit 130 may switch the corresponding node to an activestate and may transmit or receive a message. In contrast, when thecorresponding node is not scheduled to perform message transmission andreception in the specific time slot, the data processing unit 130 mayswitch the corresponding node to a sleep mode state, thereby reducingpower.

The scheduling apparatus 100 according to an embodiment uses the RPLprotocol and the TSCH-based 802.15. 4e protocol in the implementation ofa network topology. Accordingly, the scheduling apparatus 100 does notrequire message transmission for separate negotiations between nodes,and thus may minimize data transmission between the nodes. Furthermore,the scheduling apparatus 100 schedules the transmission and receptionpoints of data based on links between nodes based on the slot frame, andtransmits data with a transmission region defined within the slot framebased on rank values, thereby minimizing collisions attributable to datatransmission between the nodes.

FIG. 2 is a diagram showing a network topology according to anembodiment of the present invention.

As shown in FIG. 2, the scheduling apparatus 100 implements a networktopology in a tree form, and nodes A to O are shown on the implementednetwork topology.

In this case, the first node A may be a sink node. The second node B andthe third node C are connected to the first node A. The fourth node Dand the fifth node E are connected to the second node B, and the sixthnode F and the seventh node G are connected to the third node C.Furthermore, the eighth node H and the ninth node I are connected to thefourth node D, and the tenth node J and the eleventh node K areconnected to the fifth node E. The twelfth node L and the thirteenthnode M are connected to the sixth node F, and the fourteenth node N andthe fifteenth node O are connected to the seventh node G.

In this case, based on the second node B, the parent node of the secondnode B is the first node A, i.e., a sink node, and the child nodes ofthe second node B are the fourth node D and the fifth node E.

Accordingly, the scheduling apparatus 100 implemented in the second nodeB may transmit data, including sensing information generated at thesecond node B itself and sensing information received from the fourthnode D and the fifth node E (or the sensing information of the childnodes H, I, J and K of the fourth node D and the fifth node E) to thefirst node A. Furthermore, the scheduling apparatus 100 implemented inthe second node B may receive data corresponding to the second node Bfrom the first node A, or may receive data to be transmitted to thefourth node D and the fifth node E (including data to be transmitted tothe child nodes H, I, J and K of the fourth node D and the fifth node E)and transmit the data to the corresponding nodes.

Furthermore, assuming that a rank is a hop count, the first node A is areference node, and the hop count value (e.g., rank value) of the firstnode A is “0.” The hop count values of the second node B and the thirdnode C are “1.” The hop count values of the fourth node D, the fifthnode E, the sixth node F, and the seventh node G are “2.” Furthermore,the hop count values of the eighth node H, the ninth node I, the tenthnode J, the eleventh node K, the twelfth node L, the thirteenth node M,the fourteenth node N, and the fifteenth node O are “3.”

FIG. 3 is a diagram showing a slot frame 200 according to an embodimentof the present invention.

As shown in FIG. 3, the slot frame 200 may be represented by channelsand time. The vertical axis represents offset values for channels, andthe lateral direction represents time offset values for time.

For example, the slot frame 200 is divided into four channel offsets andsix time offsets. In this case, the slot frame 200 is illustrative, andmay have a different number of channel offsets and a different number oftime offsets. Furthermore, a time interval corresponding to a singletime offset may have a value of about 10-20 msec. The time interval maybe set to various different values based on the implementation of theapparatus or network.

Accordingly, the slot frame 200 may include cells each defined by asingle channel offset and a single time offset, and may be composed of24 (4 (M)*6 (Z)) cells. For example, as for the cells 210 and 220 of theslot frame 200, the first cell 210 may have a channel offset value of 0and a time offset value of 1, and may be represented as (0, 1).Furthermore, the second cell 220 may have a channel offset value of 2and a time offset value of 3, and may be presented by (2, 3).

In the network topology configured according to the present invention,each of the nodes may transmit data at a scheduled transmission time byusing the slot frame shown in FIG. 3.

Accordingly, the scheduling apparatus 100 proposed by the presentinvention may perform the scheduling operation of allocating cells fordata transmission at each of the nodes. This enables the schedulingapparatus 100 to determine the time to transmit or receive data to andfrom a parent node and the time to transmit or receive data to and froma child node.

FIG. 4 is a flowchart showing a scheduling method according to anembodiment of the present invention.

The scheduling method according to the embodiment shown in FIG. 4includes steps that are processed in a time sequence by the schedulingapparatus 100 shown in FIG. 1. Accordingly, the descriptions that areomitted in the following but have been given in connection with thescheduling apparatus 100 shown in FIG. 1 may be applied to thescheduling method according to the embodiment shown in FIG. 4.

As shown in FIG. 4, at step S310, the scheduling apparatus 100configures a network topology in a tree form. The network topology in atree form may be generated based on a sink node. In the case where rankvalues are set based on hop counts in the network topology, assumingthat the rank value of the sink node is 0, the rank values of nodesconnected to the sink node by using the sink node as a parent nodebecome 1, the rank values of nodes connected to a node having a rankvalue of 1 by using nodes having a rank value of 1 as parent nodesbecome 2, and the rank values of nodes connected to a node having a rankvalue of 2 by using nodes having a rank value of 2 as parent nodesbecome 3.

In the network topology in a tree form, a single node in which thescheduling apparatus 100 has been configured may be connected to aparent node and child nodes, and the scheduling apparatus 100 maytransmit data only via the connected nodes.

The network topology in a tree form is shown in FIG. 2 as an example.

At step S320, the scheduling apparatus 100 schedules data transmissionover an uplink and a downlink based on a slot frame. The schedulingapparatus 100 performs scheduling adapted to allocate the cells of theslot frame to a corresponding node for the purpose of transmitting andreceiving data. In this case, the scheduling may be classified intouplink scheduling and downlink scheduling.

For example, the scheduling apparatus 100 may perform receptionscheduling for an uplink by using Equation 1 below:

TimeOffset=(NodeRank%2)*(Z/2)+Hash(NodeID+ChildID+SlotframeID)%(Z/2)

ChannelOffset=Hash(ChildID+SlotframeID)%M   (1)

In Equation 1, TimeOffset denotes a time offset, and ChannelOffsetdenotes a channel offset. NodeRank denotes the rank of a node, andNodeID denotes the ID of a node currently being scheduled. Furthermore,ChildID denotes the ID of a child node, and SlotframeID denotes the IDof a slot frame. Z denotes the length of a single slot frame or thevalue of all time offsets constituting the slot frame, and M denotes thenumber of channel offsets constituting the single slot frame or thevalue of all channel offsets constituting the slot frame. Furthermore, %denotes a modular operation, * denotes a multiplication operation, /denotes a division operation, and Hash ( ) denotes a hash function.

The scheduling apparatus 100 may schedule cells (determined based on thetime offset and channel offset of Equation 1) based on the datareception over the uplink at the corresponding node via the receptionscheduling for the uplink.

The scheduling apparatus 100 may perform transmission scheduling for anuplink by using Equation 2 below:

TimeOffset=(ParentRank%2)*(Z/2)+Hash(ParentID+NodeID+SlotframeID)%(Z/2)

ChannelOffset=Hash(NodeID+SlotframeID)%M   (2)

In this case, ParentRank denotes the rank of a parent node, and ParentIDdenotes the ID of the parent node. For descriptions of the other IDs andsymbols, see the descriptions of the IDs and symbols of Equation 1.

The scheduling apparatus 100 may schedule cells (determined based on thetime offset and channel offset of Equation 2) based on data transmissionover the uplink at the corresponding node via the transmissionscheduling for the uplink.

The scheduling apparatus 100 may perform reception scheduling for adownlink by using Equation 3 below:

TimeOffset=(ParentRank%2)*(Z/2)+Hash(ParentID+SlotframeID)%(Z/2)

ChannelOffset=Hash(ParentID+SlotframeID)%M   (3)

In this case, for descriptions of the IDs and symbols of Equation 3, seethe descriptions of the IDs and symbols of Equations 1 and 2.

The scheduling apparatus 100 may schedule cells (determined based on thetime offset and channel offset of Equation 3) based on data receptionover the downlink at the corresponding node via the reception schedulingfor the downlink.

The scheduling apparatus 100 may perform transmission scheduling for adownlink by using Equation 4 below:

TimeOffset=(NodeRank%2)*(Z/2)+Hash(NodeID+SlotframeID)%(Z/2)

ChannelOffset=Hash(NodeID+SlotframeID)%M  (4)

In this case, for descriptions of the IDs and symbols of Equation 3, seethe descriptions of the IDs and symbols of Equations 1 and 2.

The scheduling apparatus 100 may schedule cells (determined by the timeoffset and channel offset of Equation 4) based on data reception overthe downlink at the corresponding node via the transmission schedulingfor the downlink.

Thereafter, once a cell in which data will be transmitted, thescheduling apparatus 100 transmits data in the scheduled cell within theslot frame at step S330. In this case, the scheduling apparatus 100 maytransmit uplink data by using an uplink slot frame, and may transmitdownlink data by using a downlink slot frame.

FIG. 5 is a diagram showing the allocation of slot frames based onuplink and downlink scheduling according to an embodiment of the presentinvention.

As shown in FIG. 5, a plurality of slot frames is shown. For example,uplink slot frames 411 and 412 and downlink slot frames 421 and 422 areshown.

For example, a case where the number of uplink slot frames 411 is “2”and the number of downlink slot frames 421 is “1,” and thus the sum K ofthe slot frames is “3” is illustrated. For example, the schedulingapparatus 100 may use modular operation in order to obtain a downlinkslot frame. In this case, the scheduling apparatus 100 may perform amodular operation (SlotframeID % K (=3)) with a current slot frame ID(SlotframeID) set to K. The scheduling apparatus 100 may determine thata slot frame for which the result of the modular operation is “0” is adownlink slot frame, and may determine that slot frames for which theresult of the modular operation is not “0” are uplink slot frames.

As described above, the scheduling apparatus 100 may classify aplurality of slot frames into uplink and downlink slot frames and thenperform transmission, and may perform scheduling operation in each ofall slot frames. A cell to be scheduled in individual slot frames may bescheduled in different forms. For example, a cell scheduled for aspecific node in a current slot frame may be scheduled for another nodein a subsequent slot frame.

The scheduling apparatus 100 may allocate a number of uplink slot frameslarger than the number of downlink slot frames. For example, the reasonfor this is that in a sensor network or the like, the amount of uplinkdata used to transmit sensing information from a general node to a sinknode is larger than the amount of downlink data that is transmitted fromthe sink node to the general node. Accordingly, the numbers of uplinkand downlink slot frames may be adjusted according to various methodsbased on the amount of data that is transmitted in the network topology.

FIG. 6 is a diagram showing cells allocated to nodes through schedulingin a network topology according to an embodiment of the presentinvention.

As shown in FIG. 6, in the network topology, individual nodes may formlinks. For example, a first region 510 and a second region 520 may bedefined in a single slot frame. The scheduling apparatus 100 mayallocate zeroth to second offsets to the first region 510, and mayallocate third to fifth offsets to the second region 520 based on thetime offsets.

In this case, based on a second node B, there are a first link l₁ formedin connection with a first node A, a second link l₂ formed in connectionwith a fourth node D, and a third link l₃ formed in connection with afifth node E.

For example, in an uplink slot frame, data over links formed by rankshaving even values (for example, the upstream data of the second link l₂and the third link l₃) may be transmitted in the first region 510, anddata over a link (for example, the upstream data of the first link l₁)formed by ranks having odd values (for example, the second node B) maybe transmitted in the second region 520.

Accordingly, the scheduling apparatus 100 may transmit uplink data overthe links 502 in the first region 510, and may transmit uplink data overthe links 501 and 503 in the second region 520. As described above, thescheduling apparatus 100 classifies data transmission at different ranksand then performs transmission, thereby performing scheduling so thatcollisions attributable to data transmission can be minimized.

In this case, although the description has been given based on theuplink, slot frames may be scheduled in the case of data transmissionover a downlink in a form similar to the form in the case of datatransmission over an uplink.

FIG. 7 is a diagram showing data flows based on uplink and downlinkscheduling at the second node shown in FIG. 6.

As shown in FIG. 7, based on a single second node B, a parent node A,and child nodes D and E are shown.

According to the RPL protocol, in a network topology, a node maygenerally have a single parent node, and may generally have at least onechild node. Alternatively, a node does not have a child node.

In the drawing, “U” denotes uplink data, i.e., an upstream, and refersto data or a packet that is transmitted in a direction from alower-level node (or a leaf node) to a first node A (i.e., a sink node).“D” denotes downlink data, i.e., a downstream, and refers to data or apacket transmitted in a direction from the sink node to lower-levelnodes (or leaf nodes D and E). Furthermore, “S” denotes the transmissionof data by a reference node B, and “R” denotes the reception of data bythe reference node B.

Accordingly, the scheduling apparatus 100 of the reference node B mayschedule the portion indicated by “U/R” by using the above-describedEquation 1, and may schedule the portion indicated by “U/S” by using theabove-described Equation 2. Furthermore, the scheduling apparatus 100may schedule the portion indicated by “D/R” by using the above-describedEquation 3, and may schedule the portion indicated by “D/S” by using theabove-described Equation 4.

As described above, the scheduling apparatus 100 of each node mayperform the cell scheduling of a subsequent slot frame by using the MACaddresses of the parent node and the child nodes before the period of anew slot frame starts. Thereafter, the scheduling apparatus 100 mayoperate in a wake-up or sleep mode based on the result of the schedulingof the slot frame, and may perform the scheduling of the new slot framewhen the period of the new slot frame starts.

FIG. 8 is a diagram showing the allocation of cells within a slot framebased on uplink and downlink scheduling at a node according to anembodiment of the present invention.

As shown in FIG. 8, a slot frame based on uplink scheduling at a secondnode B is shown. In this case, the rank of a first node A is “0,” therank of the second node B is “1,” and the ranks of a fourth node D and afifth node E are “2.” As described above, a single node, for example,the second node B, is different in the rank value from the parent node Aor child nodes D and E by 1. The parent node A has a rank value smallerthan the second node B's own rank value by 1, and the child nodes D andE have a rank value smaller than the second node B's own rank value by1.

As described above, since a slot frame is divided and scheduled based onrank values, the scheduling apparatus of the second node B receives dataover a corresponding channel (but does not transmits data) in the timeinterval during which the second node B receives a message, i.e., thefirst region 510, and the scheduling apparatuses of the parent node Aand the child nodes B and C receive data over the corresponding channel(but do not transmit data) in a time interval during which the secondnode B transmits a message, i.e., the second region 520. In this case,although the case where the slot frame is divided into two regions,i.e., the first region 510 and the second region 520, based on the timehas been described as an example, the first region 510 and the secondregion 520 are defined based on various different criteria, or the slotframe is divided into two or more regions.

In this case, a node Node is the second node B, a parent Parent is thefirst node A, and children are third nodes D and E. Accordingly, therank Rank of the second node B, i.e., a current node, has a rank valueof 1. Furthermore, a node rank NodeRank has a value of 1, a parent rankParentRank has a value of 0, and a child rank ChildRank has a value of2.

Furthermore, the length Z of the slot frame Slotframe has a value of 6,and the number M of channel offsets has a value of 4.

Meanwhile, the scheduling apparatus 100 may obtain the ID of the currentslot frame by using an ASN value. For example, when the ASN value is 93,the value of the slot frame ID SlotframeID starting from 0 is 15obtained by dividing 93 by a slot frame length of 6 and then roundingdown. In other words, when the ASN value is 93, the slot frame of a 16thslot frame period may be scheduled.

For example, the MAC address value of the second node B may be 2943(NodeID), the MAC address value of the first node A may be 9483(ParentID), the MAC address value of the fourth node D may be 1342(ChildID), and the MAC address value of the fifth node E may be 6296(ChildID).

In this case, when uplink reception scheduling is performed based onEquation 1, this may be represented by Equation 5 below:

TimeOffset=(0%2)*(6/2)+Hash(2943+ChildID+93)%(6/2)=0*3+Hash(ChildID+3036)%3

ChannelOffset=Hash(ChildID+93)%4   (5)

In this case, when 1342, i.e., the childID of the fourth node D, isapplied, the scheduling apparatus 100 may obtain (2, 3) in which a timeoffset is 2 and a channel offset is 3. Furthermore, when 1342, i.e., thechildID of the fourth node D, is applied, the scheduling apparatus 100may obtain (2, 3) in which a time offset is 2 and a channel offset is 3.

Furthermore, when uplink transmission scheduling is performed based onEquation 2, this may be represented by Equation 6 below:

TimeOffset=(1%2)*(6/2)+Hash(9483+2943+93)%(6/2)=1*3+Hash(12519)%3=3

ChannelOffset=Hash(2943+93)%4=0   (6)

As described above, the scheduling apparatus 100 may perform downlinkreception scheduling, and thus may obtain a time offset of 3 and achannel offset of 0.

Accordingly, the scheduling apparatus 100 may schedule data from thechild nodes D and E in cells (2, 3) and (1, 1), respectively, byperforming transmission scheduling for the uplink, and may performscheduling in a cell (3, 0) by performing transmission scheduling forthe uplink.

This is illustrative. The scheduling apparatus 100 may allocate cells inthe slot frame for reception and transmission scheduling for a downlinkby using Equations 3 and 4, as in the case of using Equations 1 and 2 ofFIG. 8.

The term “˜ unit” used herein may refer to a software component, or ahardware component, such as, a field programmable gate array (FPGA) oran application specific integrated circuit (ASIC), and the “˜ unit”performs at least one function or operation. However, the “˜ unit” isnot meant to be limited to the software or hardware. The “˜ unit” may beconfigured to reside on an addressable storage medium and to run one ormore processors. Therefore, as an example, the “˜ unit” includes acomponent such as a software component, an object-oriented softwarecomponent, a class component, or a task component, a process, afunction, an attribute, a procedure, a subroutine, a segment of programcode, a driver, firmware, microcode, circuitry, data, a database, a datastructure, a table, an arrays, or a variable.

The function provided by the “˜ unit” may be provided separately by oneor more components, or may be incorporated with one or more functions.

Furthermore, the “˜ unit” may be implemented to run one or more CPUspresent in a device or security multimedia card.

Furthermore, the method according to an embodiment of the presentinvention may be implemented as a computer program (or a computerprogram product) including computer-executable instructions. Thecomputer program includes programmable machine instructions that can beprocessed by a processor, and may be implemented as a high-levelprogramming language, an object-oriented programming language, anassembly language, a machine language, or the like. Furthermore, thecomputer program may be stored on a computer-readable storage medium(for example, memory, a hard disk, a magnetic/optical medium, asolid-state drive (SSD), or the like).

The method according to an embodiment of the present invention may beimplemented in such a way that the above-described computer program isexecuted by a computing device. The computing device may include atleast some of a processor, memory, a storage device, a high-speedinterface connected to the memory and a high-speed extension port, and alow-speed interface connected to a low-speed bus and the storage device.The above components are connected to each other via various buses, andmay be mounted on a common mother board or by another appropriatemethod.

In this case, the processor may process instructions in the computingdevice. Such instructions may be instructions that are stored in memoryor a storage device to display graphic information adapted to provide aGraphic User Interface (GUI) onto an external input/output device, e.g.,a display connected to a high-speed interface. As another embodiment, aplurality of processors and or a plurality of buses may be used inconjunction with a plurality of pieces of memory or a plurality ofmemory forms. Furthermore, the processors may be implemented as achipset composed of chips including a plurality of analog or digitalindependent processors.

Furthermore, the memory stores information inside the computing device.As an example, the memory may be composed of a volatile memory unit or aset of volatile memory units. As another example, the memory may becomposed of a nonvolatile memory unit or a set of nonvolatile memoryunits. Furthermore, the memory may be another type of computer-readablemedium, such as a magnetic or optical disk.

Furthermore, the storage device may provide a mass storage space to thecomputing device. The storage device may be a computer-readable mediumor a configuration including a computer-readable medium. For example,the storage device may include devices inside a storage area network(SAN) or another configuration. The storage device may be a floppy diskdevice, a hard disk device, an optical disk device, a tape device, flashmemory, another semiconductor memory device similar thereto, or anotherdevice array.

According to the above-described present invention, there may beproposed the scheduling apparatus and method that configure a networktopology in a tree form and do not perform any negotiation between nodeswithin a network based on the characteristics of the structure.

Furthermore, according to the above-described present invention, theremay be proposed the scheduling apparatus and method that performlink-based scheduling for an uplink and a downlink based on ranks inorder to avoid collisions between uplink data and downlink data, therebyminimizing collisions attributable to data transmission between nodes ina network.

The above description of the present invention is illustrative. It willbe apparent to those having ordinary knowledge in the art to which thepresent invention pertains that the above-described embodiments may beeasily modified into other forms without departing from the technicalspirit or essential features of the present invention. Therefore, itshould be understood that the above-described embodiments areillustrative in all aspects and are not limitative. For example, eachcomponent described as being in a single form may be practiced in adistributed form. In the same manner, components described as being in adistributed form may be practiced in an integrated form.

The scope of the present invention is defined by the attached claims,rather than the above detailed description. Furthermore, allmodifications and variations derived from the meanings, scope andequivalents of the claims should be construed as falling within thescope of the present invention.

What is claimed is:
 1. A scheduling apparatus, comprising: a networktopology configuration unit configured to configure a network topologythat connects nodes to which rank values have been allocated based on asink node; and a scheduling unit configured to schedule datatransmission over an uplink and a downlink in a first region and asecond region defined in each slot frame based on the rank valuesobtained based on the sink node; wherein the first region and the secondregion have different time offsets within the slot frame.
 2. Thescheduling apparatus of claim 1, wherein the network topologyconfiguration unit configures a network topology in a tree form byconnecting nodes, having received respective beacon signals transmittedby the sink node at intervals of a predetermined period, to a time slotchannel scheduling network formed by the sink node.
 3. The schedulingapparatus of claim 2, wherein the network topology configuration unitconfigures the network topology in a tree form by using an IPv6 routingprotocol for low-power lossy networks (RPL) protocol in a network layerand a time slot channel scheduling-based 802.15.4e protocol in a linklayer.
 4. The scheduling apparatus of claim 1, wherein the schedulingunit transmits data in the first region when a rank value obtained basedon the sink node is an even rank, and transmits data in the secondregion when a rank value obtained based on the sink node is an odd rank.5. The scheduling apparatus of claim 4, wherein the scheduling unitgenerates a number of slot frames for the uplink and a number of slotframes for the downlink at a preset ratio, and sets the number of slotframes for the uplink to a value larger than the number of slot framesfor the downlink.
 6. The scheduling apparatus of claim 4, wherein thescheduling unit comprises: an uplink scheduler configured to scheduletransmission and reception of uplink data; and a downlink schedulerconfigured to schedule transmission and reception of downlink data. 7.The scheduling apparatus of claim 6, wherein the uplink schedulerperforms the reception scheduling for the uplink by scheduling a timeoffset and a channel offset within the slot frame based on Equationbelow:TimeOffset=(NodeRank%2)*(TimeOffset/2)+Hash(NodeID+ChildID+SlotframeID)%(TimeOffset/2)ChannelOffset=Hash(ChildID+SlotframeID)%the number ofchannels  [Equation] where % denotes a modular operation, * denotes amultiplication operation, / denotes a division operation, and Hash ( )denotes a hash function.
 8. The scheduling apparatus of claim 6, whereinthe uplink scheduler performs the transmission scheduling for the uplinkby scheduling a time offset and a channel offset within the slot framebased on Equation below:TimeOffset=(ParentRank%2)*(TimeOffset/2)+Hash(ParentID+NodeID+SlotframeID)%(TimeOffset/2)ChannelOffset=Hash(NodeID+SlotframeID)%the number of channels where %denotes a modular operation, * denotes a multiplication operation, /denotes a division operation, and Hash ( ) denotes a hash function. 9.The scheduling apparatus of claim 6, wherein the downlink schedulerperforms the reception scheduling for the downlink by scheduling a timeoffset and a channel offset within the slot frame based on Equationbelow:TimeOffset=(ParentRank%2)*(TimeOffset/2)+Hash(ParentID+SlotframeID)%(TimeOffset/2)ChannelOffset=Hash(ParentID+SlotframeID)%the number ofchannels  [Equation] where % denotes a modular operation, * denotes amultiplication operation, / denotes a division operation, and Hash ( )denotes a hash function.
 10. The scheduling apparatus of claim 6,wherein the downlink scheduler performs the transmission scheduling forthe downlink by scheduling a time offset and a channel offset within theslot frame based on Equation below:TimeOffset=(ParentRank%2)*(TimeOffset/2)+Hash(ParentID+SlotframeID)%(TimeOffset/2)ChannelOffset=Hash(ParentID+SlotframeID)%the number ofchannels  [Equation] where % denotes a modular operation, * denotes amultiplication operation, / denotes a division operation, and Hash ( )denotes a hash function.
 11. A scheduling method for a schedulingapparatus, the scheduling method comprising: configuring a networktopology that connects nodes to which rank values have been allocatedbased on a sink node; and scheduling data transmission over an uplinkand a downlink in a first region and a second region defined in eachslot frame based on the rank values obtained based on the sink node;wherein the first region and the second region have different timeoffsets within the slot frame.
 12. The scheduling method of claim 11,wherein configuring the network topology comprises configuring a networktopology in a tree form by connecting nodes, having received respectivebeacon signals transmitted by the sink node at intervals of apredetermined period, to a time slot channel scheduling network formedby the sink node.
 13. The scheduling method of claim 12, whereinconfiguring the network topology comprises configuring the networktopology in a tree form by using an IPv6 routing protocol for low-powerlossy network (RPL) protocol in a network layer and a time slot channelscheduling-based 802.15.4e protocol in a link layer.
 14. The schedulingmethod of claim 11, wherein scheduling the data transmission over theuplink and the downlink comprises performing scheduling in such a way asto transmit data in the first region when a rank value obtained based onthe sink node is an even rank and to transmit data in the second regionwhen a rank value obtained based on the sink node is an odd rank. 15.The scheduling method of claim 14, wherein scheduling the datatransmission over the uplink and the downlink further comprisesgenerating a number of slot frames for the uplink and a number of slotframes for the downlink at a preset ratio, and setting the number ofslot frames for the uplink to a value larger than the number of slotframes for the downlink.
 16. The scheduling method of claim 14, whereinscheduling the data transmission over the uplink and the downlinkfurther comprises performing the reception scheduling for the uplink byscheduling a time offset and a channel offset within the slot framebased on Equation below:TimeOffset=(NodeRank%2)*(TimeOffset/2)+Hash(NodeID+ChildID+SlotframeID)%(TimeOffset/2)ChannelOffset=Hash(ChildID+SlotframeID)%the number ofchannels  [Equation] where % denotes a modular operation, * denotes amultiplication operation, / denotes a division operation, and Hash ( )denotes a hash function.
 17. The scheduling method of claim 14, whereinscheduling the data transmission over the uplink and the downlinkfurther comprises performing the transmission scheduling for the uplinkby scheduling a time offset and a channel offset within the slot framebased on Equation below:TimeOffset=(ParentRank%2)*(TimeOffset/2)+Hash(ParentID+NodeID+SlotframeID)%(TimeOffset/2)ChannelOffset=Hash(NodeID+SlotframeID)%the number of channels where %denotes a modular operation, * denotes a multiplication operation, /denotes a division operation, and Hash ( ) denotes a hash function. 18.The scheduling method of claim 14, wherein scheduling the datatransmission over the uplink and the downlink further comprisesperforming the reception scheduling for the downlink by scheduling atime offset and a channel offset within the slot frame based on Equationbelow:TimeOffset=(ParentRank%2)*(TimeOffset/2)+Hash(ParentID+SlotframeID)%(TimeOffset/2)ChannelOffset=Hash(ParentID+SlotframeID)%the number ofchannels  [Equation] where % denotes a modular operation, * denotes amultiplication operation, / denotes a division operation, and Hash ( )denotes a hash function.
 19. The scheduling method of claim 14, whereinscheduling the data transmission over the uplink and the downlinkfurther comprises performing the transmission scheduling for thedownlink by scheduling a time offset and a channel offset within theslot frame based on Equation below:TimeOffset=(ParentRank%2)*(TimeOffset/2)+Hash(ParentID+SlotframeID)%(TimeOffset/2)ChannelOffset=Hash(ParentID+SlotframeID)%the number ofchannels  [Equation] where % denotes a modular operation, * denotes amultiplication operation, / denotes a division operation, and Hash ( )denotes a hash function.